In order to determine the quality of coatings, various properties of the coatings are tested. Such coatings are for example lacquers on various surfaces, such as metals, plastics, glass, wood, etc. The tested mechanical properties include for example adhesion, elasticity, hardness, scratch resistance, or stone impact resistance of the lacquer. In general, the characterization of many testing methods takes place through the optical assessment of damages caused by a defined mechanical stress. Thus, for example the adhesion of a lacquer is usually tested using a cross cutting test. Here, as a rule the evaluation is carried out through visual observation and classification by the tester.
In the case of clear lacquers, the difference from the substrate is very small, so that even a visual evaluation by the tester is very difficult. U.S. Patent Application Publication No. 2004/0149026 describes mixing a fluorescent dye with the clear lacquer, so that fluorescent and non-fluorescent surfaces can be distinguished. However, a disadvantage of the admixture of a fluorescent dye is that the properties of the lacquer may be changed by the admixture.
In other conventional methods for determining the mechanical properties, the evaluation is carried out by the tester, and the methods are more empirical in nature. The evaluation is oriented towards clear differences in color. Evaluations of glossy or matte clear lacquers on glossy or matte metal substrates are limited by the slight color differences. A coloration of the clear lacquer due to the admixture of fluorescent dyes or other dyes in order to make the lacquer visible may change the hardening and/or the other properties of the lacquer due to interaction with the lacquer or with a component of the lacquer, e.g. the initiator. In addition, attention must be paid to solubility effects due to precipitation of the dye during the polymerization, and concomitant effects on the structure of the lacquer layer. In addition, a plurality of tests are frequently carried out for one coating, and the results may be altered by the admixture of the dye.